1. Field of the Invention
The present invention relates to a switch module used for key portions of portable devices such as mobile phones and notebook PCs.
2. Description of the Related Art
In recent years, it has been often seen that portable devices such as mobile phones and notebook PCs have a configuration in which LEDs (Light Emitting Diodes) are provided, as light source elements, on a board of a switch module disposed to face the back side of key portions. By thus providing the LEDs on the board of the switch module, light can be suitably irradiated onto a part of the key portions where light irradiation is required, from the switch module side. Furthermore, in recent years, a configuration is proposed in which a light guide plate is provided between key portions and a board of a switch module and light emitted from LEDs is guided to the light guide plate, whereby light is suitably irradiated onto a plurality of key portions. With this configuration, by combining the LEDs and the light guide plate, the number of LEDs can be reduced, enabling to achieve a reduction in manufacturing cost and power consumption.
Now, with reference to FIGS. 4A and 4B, a schematic configuration of a conventional switch module in which LEDs and a light guide plate are combined will be described. FIG. 4A is a schematic cross-sectional view of a conventional switch module and FIG. 4B is a schematic diagram showing the operation of a switch member 102 configured to be deformable. As shown in the drawings, in the conventional switch module, aboard 100 is provided in a position where the board 100 faces key portions 110. The board 100 is provided with wiring lines 101, electrodes 103, and metal domes 102 serving as switch members that cover their corresponding electrodes 103.
In addition, a dome sheet 105 serving as a protective member that mechanically protects the metal domes 102 is provided on surfaces of the metal domes 102. Alight guide plate 104 that guides light emitted from an LED 120 is provided between the dome sheet 105 and the key portions 110. Note that the light guide plate 104 is formed of acrylic, polycarbonate, or silicon rubber, and in portions of the light guide plate 104 that allow light to be reflected in a direction of the key portions 110, projections and recesses (reflecting portions) are formed by dot printing, a heat treatment, cutting processing, etc.
With this configuration, by a key portion 110 moving downward in FIG. 4A and a corresponding key top 110a thereby coming into contact by pressure with a corresponding metal dome 102, with the light guide plate 104 and the dome sheet 105 being sandwiched therebetween, the metal dome 102 is deformed and thus a part of the metal dome 102 comes into contact with a corresponding electrode 103. As a result, a corresponding wiring line 101 is electrically connected to the electrode 103 through the metal dome 102. This state is shown in FIG. 4B. Note that in FIG. 4B the light guide plate 104 and the dome sheet 105 are omitted for easy description of the operation of the metal dome 102.
However, the conventional switch module has the following problems.
<Problem 1: Difficulty in Slimming Down>
In recent years, there has been an increasing demand for slimming down and an improvement in design of portable devices. To meet the demand, a switch module needs to be slimmed down. However, in the configuration of the above-described conventional switch module, since the light guide plate 104 and the dome sheet 105 are provided between the key portions 110 and the board 100, it is difficult to slim down the switch module.
<Problem 2: Insufficient Click Feeling>
In general, in a portable device having key portions, the key portions are required to have a sufficient click feeling. The sensitivity of click feeling can be converted into numbers by “click rate (%)”. Namely, the higher the “click rate (%)” is, the more sufficient click feeling is obtained. FIG. 3B shows the definition of the “click rate (%)”. When the key portion is depressed (when the stroke of the key portion increases), a load on the key portion also increases to deform the switch member. When the load reaches a certain value, the switch member starts to be deformed. The load obtained at this time is F1. When the load reaches F1, thereafter, while the switch member is deformed, the key portion moves. Thus, with an increase in the stroke of the key portion, the load decreases. The minimum load obtained at this time is F2. Using F1 and F2 described here, the click rate is defined such that “click rate (%)=(F1−F2)/F1×100”.
In the configuration of the above-described conventional switch module, since the light guide plate 104 and the dome sheet 105 are provided between the key portions 110 and the board 100, the “click rate (%)” decreases accordingly, and thus, a sufficient click feeling cannot be obtained. Hence, user's error operation and a reduction in operability are caused.
<Problem 3: Increase in Cost>
In the configuration of the above-described conventional switch module, since the light guide plate 104 for guiding light emitted from the LED 120 is required, the number of components of the switch module increases and also an assembly process becomes complex. As a result, an increase in manufacturing cost is brought about. To cope with the above-described problem of click feeling, for example, measures of providing projections on the surfaces of the light guide plate 104 and the metal domes 102 may be considered. However, in this case, too, since special processing is required to provide the projections, an increase in manufacturing cost is brought about.
Note that although there is disclosed, as one conventional art, a configuration of a membrane switch including a lighting display unit, in this case, since members corresponding to the above-described metal domes are not provided, a sufficient click feeling cannot be obtained. In addition, since a technique in which electric circuit parts are insert-molded using a transparent resin, etc., is used, it is difficult to slim down a switch module. In addition, although there is disclosed, as another conventional art, a technique in which a membrane switch having a polydome sheet is formed using a transparent FPC (Flexible Printed Circuit) having light transmittance, since a light guide plate is provided below a switch sheet, a switch module cannot be slimed down.